FDC37C78 Datasheet, PDF (18/82 Pages) SMSC Corporation – Floppy Disk Controller

MAIN STATUS REGISTER
Address 3F4 READ ONLY
The Main Status Register is a read-only register
and indicates the status of the disk controller. The
Main Status Register can be read at any
7
6
5
4
RQM
DIO
NON CMD
DMA BUSY
time. The MSR indicates when the disk controller
is ready to receive data via the Data Register. It
should be read before each byte transferring to or
from the data register except in DMA mode. NO
delay is required when reading the MSR after a
data transfer.
3
DRV3
BUSY
2
DRV2
BUSY
1
DRV1
BUSY
0
DRV0
BUSY
BIT 0 - 3 DRVx BUSY
These bits are set to 1s when a drive is in the seek
portion of a command, including implied and
overlapped seeks and recalibrates.
BIT 4 COMMAND BUSY
This bit is set to a 1 when a command is in
progress. This bit will go active after the command
byte has been accepted and goes inactive at the
end of the results phase. If there is no result
phase (Seek, Recalibrate commands), this bit is
returned to a 0 after the last command byte.
BIT 5 NON-DMA
This mode is selected in the SPECIFY command
and will be set to a 1 during the execution phase of
a command. This is for polled data transfers and
helps differentiate between the data transfer phase
and the reading of result bytes.
BIT 6 DIO
Indicates the direction of a data transfer once a
RQM is set. A 1 indicates a read and a 0 indicates
a write is required.
BIT 7 RQM
Indicates that the host can transfer data if set to a
1. No access is permitted if set to a 0.
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